None of the 50 nuclear reactors in Japan is online, meaning about 20 percent of the country's power capacity isn't available.
The country's crude and fuel oil demand for power generation is expected to be around 700,000 barrels per day from July through September because of the nuclear power shortage, the Platts news service reports.
Japan last month shut its last operating nuclear reactor for maintenance, leaving the country without nuclear power for the first time in more than 40 years.
A magnitude-9 earthquake and tsunami struck northeastern Japan in March 2011, crippling the country's Fukushima Daiichi nuclear power plant and forcing Tokyo to pursue more non-nuclear forms of energy.
Japanese Prime Minister Yoshihiko Noda is considering whether to allow the restart of two reactors as summer approaches, Platts adds.